Not Applicable.
The present invention relates to drilling jars that are connected in-line in a drill string or work over string and that are used to deliver jarring impacts during drilling or work over operations such as fishing.
Drilling jar""s and in particular Houston Engineers"" Hydra-Jar(copyright) tools are used to free stuck drill strings or to recover stuck drill string components during drilling or workover operations. The jar""s provide an impact blow (hence the name jar) either in the up or down directions. The driller can control the jarring direction, impact intensity and jarring times from the rig floor. The magnitude and direction of the load used to initiate the impact blow (jar) achieve this control. Examples of hydraulic jars are disclosed in U.S. Pat. Nos. 5,431,221, 5,174,393, 5,595,244, 5,447,196, 5,503,228, 5,595,253 and such patents are incorporated herein by reference.
FIG. 1 shows a cross section through detent area 11 of prior art jar 10. Upward force arrow 13 is shown applied to mandrel 12 of jar 10. This force is transmitted to outer cylindrical housing 14 by a resulting increase in pressure in the hydraulic fluid that is contained in upper chamber 16 between outer cylindrical housing 14 and mandrel 12.
The magnitude of the pressure in upper chamber 16 is directly proportional to the magnitude of the force applied to mandrel 12. This high-pressure fluid is allowed to flow through orifice 18 to a lower chamber 20. The result of this fluid flow is a relative axial movement between outer housing 14 and mandrel 12. When this relative axial movement is sufficient to place orifice 18 in juxtaposition to relief area 17 of outer housing 14 a sudden release of high pressure fluid occurs which results in a impact blow being delivered to the xe2x80x9cknockerxe2x80x9d part of the jar (not shown). The xe2x80x9cknockerxe2x80x9d is usually located at the upper most end of the Drilling Jar.
The present invention provides a drilling jar comprising a mandrel with a shoulder extending radially outward that defines at least one openable and closeable orifice therethrough. An outer housing is slidably disposed about the mandrel to define an upper chamber above the shoulder and a lower chamber below the shoulder. A magnetorestriction material responds to a predetermined pressure in the upper chamber to open the at least one orifice in the shoulder to allow rapid pressure communication between the upper and lower chambers.